prop question

[rathrbfishin]

I have a 98 Sea Stealth , with a 98 Yamaha 90. With the average load of boat, motor, gas, equip and people @ wot I'm at 4900-5000 rpm's. I have a 17 pitch prop. I have read that if I prop down to a 15 pitch I will gain around 400 rpm's which brings me to the high end of my motors operating range ( 4500-5500) My question is by gaining those rpm's will that inturn increase my speed?

 

[QC]

Re: prop question

Usually they are fastest in the middle to lower end of the range. The 15" will improve your hole shot, but could slightly decrease your top speed. Also, yoo could end up in an overspeed condition if the boat was lightly loaded.<br /><br />Your existing prop sounds right. If you don't have a spare and would like to experiment then do it.<br /><br />Check out the WOT and Propeller threads in the Engine FAQ section.

 

[SKIEB]

Re: prop question

I have a problem getting on plane with my 200 optimax mercury. I have a 19' NITRO CDX. The prop is 4 blade 25 pitch. When it comes up out of the hole and starts to lay down the prop breaks loose and the motor over rev's. I have to do this a couple of times before I can get to plane. The prop is not broken. I can top out at 80 MPH. after getting on plane. Is there something I need to do to the prop to get the thing to stop washing out.

 

[Dhadley]

Re: prop question

Welcome!!<br /><br />What brand prop is it? And what diameter?

 

[chuckz]

Re: prop question

Not a prop problem, either a trim or motor mounting problem. Provide details of how your engine is set-up and one of the go fast bass boat boys will help you.

 

[rathrbfishin]

Re: prop question

the motor is mounted all the way down. cavitation plate is even with bottom of hull. If I raise the engine will that increase my rpm's ????

 

[JB]

Re: prop question

Outboard Non-repair topic

 

[Dhadley]

Re: prop question

Going down in pitch rarely gains speed. Work with the set up. We only go to smaller pitch as an absolute last resort. Your motor is all the way down so you can, most likely, go up to gain performance. We work with slip percentages. To gain efficiency we reduce the slip %.<br /><br />If your prop is an aluminum you may not be able to raise the motor as far as a ss prop but you will certianly gain something.

 

[chuckz]

Re: prop question

Sorry, I was responding to SKIEB. SKIEB should problably start a new thread instead of hijacking this one.

 

[umblecumbuz]

Re: prop question

If your prop is an aluminum you may not be able to raise the motor as far as a ss prop but you will certianly gain something.

Dhadley,<br />That's an interesting remark about raising the engine more if using a s/s prop?<br /><br />Why can that be? I don't understand.

 

[rathrbfishin]

Re: prop question

It is a ss prop. When I purchased the boat the motor was raised all the way up. That caused the boat to porpoise real bad, so that's why I lowered it. I still have a problem when I make sharp turns , prop seems to "blow out".

 

[Dhadley]

Re: prop question

Stillfishing, thats the nature of the ss. They can build more technology or "bite" into it and it will hold. The aluminum will flex more and it gets too costly to use agressive shapes. <br /><br />Rathrbfishin, it sounds like the prop may be worn some and losing the tip cup. What brand is it?

 

[rathrbfishin]

Re: prop question

PowerTech.

 

[Dhadley]

Re: prop question

Thats a decent prop. If the cup is worn at the tip area it will act as you describe. Look at it real close and see where the cup ends (starting at the hub). You will probably be able to feel it better than see it.

 

[rathrbfishin]

Re: prop question

I'm no expert , but it looks worn to me. Is that something a prop shop can fix (re-cup).

 

[Dhadley]

Re: prop question

Yes. A good shop will weld material back on and then reshape to original design. They must have the right pitch blocks but good ones do.

 

[lyra]

Re: prop question

First thing to check will be engine height, prop brand, hub size(small hub or big hub). If merc with pvs maybe to much ventilation.